As one can ascertain from the prior art, there is a need for high temperature operation in regard to pressure transducers. Pressure transducers capable of operating at high temperatures while further being of small physical dimensions are extremely desirable for use in many areas such as satellite applications, nuclear power, chemical processing, aerodynamics, engine testing, and so on. The prior art is replete with many techniques for fabricating such transducers. Certain techniques use organic epoxy adhesive to bond sensors to a metal diaphragm. Other techniques employ monolithic devices which are sensors fabricated integrally with a silicon diaphragm. Such integral configuration permitted higher temperature operation but at temperatures at about 350.degree. F. the isolation between the sensors and the substrate deteriorated. This is caused by thermally generated carriers which serve to short circuit the sensors to the substrate. Hence, in order to circumvent such problems, there were sensors fabricated in the prior art which were dielectrically isolated. For example, see U.S. Pat. No. 3,800,264 entitled HIGH TEMPERATURE TRANSDUCERS AND HOUSING INCLUDING FABRICATION METHODS by A. D. Kurtz et al. and assigned to Kulite Semiconductor Products, Inc., the assignee herein. See also U.S. Pat. No. 3,930,823 issued on Jan. 6, 1976 to A. D. Kurtz et al. and entitled HIGH TEMPERATURE TRANSDUCERS AND HOUSING INCLUDING FABRICATION METHODS. Thus as one can ascertain, previous monolithic piezoresistive pressure transducers which employed silicon stress sensors isolated from the force collecting structure by PN junctions suffer from the problem that the isolation between the stress sensor network and the force collector deteriorates as a function of temperature. The newer class of devices which provide dielectric isolation of the sensor from the diaphragm as, for example, indicated in the above-noted references has provided devices that can operate at temperatures in excess of 500.degree. C. However, above 600.degree. C. the silicon sensing network as well as the silicon force collector, undergo significant plastic deformation rendering the device useless as a pressure transducer.
Hence, it is an object of the present invention to provide a sensor apparatus which is operable at higher temperatures.
It is a further object of the present invention to provide a sensor which provides a higher isolation with temperature as well as capable of operating at higher temperatures before plastic deformation will occur.